You can easily earn 4501 coins every 8 minutes in Plants vs Zombies Garden Warfare 2 doing absolutely NOTHING.
1) Choose either Herbal Assault or Gardens and Graveyards,
2) In Team Setup, set both teams to None
3) Choose CRAAAAAAZY Difficulty
4) Choose the defensive team
5) After 7 minutes, you will be 4501 coins richer!
This is by far the easiest coin grind strategy I have seen since launch.